At 4:00 p.m. on September 1, 1975, 17 cars of a Chicago, Rock Island and Pacific Railroad train, No. 81A31, derailed at the frog of a facing point switch on the main line near Des Moines, Iowa. The train was descending a 1-percent grade on a 1-degree curve. Eleven of the derailed cars contained liquefied petroleum gas (LPG). Fire and explosions ensued; the LPG was consumed and three persons were injured.